My father's passing was unexpected - so when I spoke, I used this, which I thought captured the impossibility of understanding something so senseless. It may not apply here, depending on circumstances:

"There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened." (from The Restaurant at the End of the Universe)

Others that are potentially useful:

"He hoped and prayed that there wasn’t an afterlife. Then he realized there was a contradiction involved here and merely hoped that there wasn’t an afterlife." (from Life, the Universe, and Everything)

"The quality of any advice anybody has to offer has to be judged against the quality of life they actually lead.” (from Mostly Harmless)

Whatever you go with, you're awesome and I'm sure your dad knew it.